Ball and socket joints transmit and absorb forces from a plurality of directions. They are used in automotive engineering, for example, in the area of the steering or track rod. Ball and socket joints of this class comprise a ball pivot, i.e., a bolt with a ball formed at an axial end, a bearing shell accommodating the ball and a housing accommodating the bearing shell and parts of the ball pivot. The ball of the ball pivot slides within the prestressed, permanently lubricated bearing shell, which is protected by the housing against moisture and dirt as well as against the escape of lubricant. In the case of use in a motor vehicle, especially the inner surfaces of the bearing shell accommodating the ball are exposed to high loads. The bearing shells are therefore manufactured, as a rule, from a metal. However, steadily increasing requirements are also imposed on comfort in modern automotive engineering, which can sometimes be met by ball and socket joints with a metallic bearing shell only insufficiently. One drawback is that structure-borne noise is transmitted from the chassis to the passenger compartment or released into the environment to an undesired extent by ball and socket joints with a metallic shell. Ball and socket joints with a plastic shell offer considerable advantages in respect to the transmission of structure-borne noise. Such joints can also meet the requirements concerning loadability in many cases if modern plastics are used. However, their drawback is that their emergency running properties are considerably limited, i.e., total failure of the ball and socket joint can be observed within a short time in case of a defect or failure of the housing seal of a corresponding ball and socket joint, as a consequence of which dirt enters the joint or the lubricant escapes from the bearing site proper, i.e., from the intermediate space between surfaces of the ball of the ball pivot and the bearing shell, which surfaces slide on one another.
A ball and socket joint with a non-metallic bearing shell, in which the bearing shell has a two-layer design, has become known from DE 103 29 804 A1. According to the solution described in that document, the two layers forming the shell have different moduli of elasticity, the outer layer located away from the ball consisting of an elastically springable material and the inner layer located close to the ball consisting of a material with a wear-resistant surface. However, aside from the reference that the bearing shell consists of a non-metallic material, no concrete data are specified concerning the materials of the two layers forming the bearing shell. It can therefore be assumed here from a manufacturing technological point of view that both layers consist of a plastic, but the plastics have different moduli of elasticity and surface strengths, because such layers consisting of different plastics can be manufactured in a two-stage injection molding process and connected to one another in a favorable manner. The requirement that the structure-borne noise be reduced is certainly also met with the use of a corresponding plastic for the inner layer for many applications. However, the problem of insufficient emergency running properties is certainly present with this solution as well, because, unlike in the case of metals, dirt, which can be observed, for example, when leaks develop in ball and socket joints in the area of the running surfaces, tend to dig into the material surface to a certain extent in the case of plastics and materials comparable to plastics. At any rate, metals thus have emergency running properties that can hardly be attained by plastics.